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Hydrogen Gas Collection Lab CE (6/6) A sample of solid magnesium ribbon, measuring approximately 2.5cm and weighing 0.037 g +/- 3% was allowed to react with an aqueous solution of hydrochloric acid

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Introduction

Conclusion and Evaluation: A sample of solid magnesium ribbon, measuring approximately 2.5cm and weighing 0.037 g +/- 3% was allowed to react with an aqueous solution of hydrochloric acid, with a concentration of 6 mol dm-3 in a 1000cm3 graduated cylinder. The sample of magnesium was wrapped in a cage constructed of copper wire, and mounted on a holed rubber stopper, which was inserted into the end of a gas measuring tube, with 14.90 cm3 +/- 0.3% of 6 mol dm-3 HCl(aq) already in the tube with the rest of the gas measuring tube being filled with tap water. The gas measuring tube was then inverted into the 1000cm3 graduated cylinder, in which there was 790 cm3 +/- 0.6% of tap water, and was allowed to react with the 6 mol dm-3 hydrochloric acid once it had descended down to where the magnesium strip lay since hydrochloric acid is denser than water (As told by teacher). This, in a vigorous reaction, produced a gas that ascended to the top of the gas measuring tube, and it can be said that it is mostly comprised of hydrogen gas, as per the following, balanced equation: Mg(s) + 2HCl(aq) --> MgCl2(aq) + H2(g) (Michigan State University, n.d.) Considering the main reactants are solid magnesium ribbon, and 6 mol dm-3 hydrochloric acid, the gas produced is hydrogen gas. The hydrochloric acid did not react with the copper wire that was holding the magnesium ribbon in place because of its position on the hydrogen side of the electrochemical series of metals (University of Siegen, n.d.). Through stoichiometric calculations conducted in the data processing section of the investigation report, it was found that the theoretical yield of hydrogen gas is 0.0015 mol, since the reaction is limited by the amount of Mg(s) (ie. it is the limiting reactant). It was found that, through using the ideal gas law and the observations recorded during the investigation (pressure, temperature, and volume) ...read more.

Middle

This means they were not produced by the reaction between the solid magnesium and 6 mol dm-3 HCl(aq) since they had not yet come in contact. Even the bubbles towards the opening end of the gas measuring tube would have been dislodged and measured as part of the hydrogen gas collected, once the reaction has started between the solid magnesium ribbon and 6 mol dm-3 HCl(aq) since the hydrogen gas produced by their reaction would bump into them, and both the hydrogen gas and the air bubbles would be counted as being part of the hydrogen gas collected by the reaction between solid magnesium ribbon and 6 mol dm-3 HCl(aq). This would mean that not all of the gas collected by the gas measuring tube during the reaction of solid magnesium ribbon and 6 mol dm-3 HCl(aq) is in fact hydrogen gas. Therefore, this would cause the volume recorded to not be representative of the amount of hydrogen gas collected, since it is not all hydrogen gas. This would have the effect of increasing the actual yield of hydrogen gas measured, and can therefore be attributed as one of the systematic errors at play during the investigation that lead to the 104% percentage yield of hydrogen gas. This source of error can be mitigated by performing a similar procedure with the source of error previously listed, except this time the gas measuring tube and its contents will be upright. This means running a cleaning utensil (pipe cleaner, etc...) down the length of the gas measuring tube once it has been filled with liquids. However, a procedural change will have to be applied: the hydrochloric acid will have to be added after the cleaning has been conducted, and therefore, only about 3/4 of the gas measuring tube should be filled - leaving enough room to add the hydrochloric acid. This remedy achieves two things: it prevents any of the hydrochloric acid from staying on the cleaning device and therefore loosing reactant, and two, it dislodges ...read more.

Conclusion

It is worth noting that there was a change in temperature noticed in the of the 790 cm3 +/- 0.6% tap water bath from before the gas measuring tube was inverted and inserted, and after the reaction had ceased between the solid magnesium ribbon attached in the copper wire structure, mounted on the holed rubber stopper and 6 mol dm-3 HCl(aq) of 0.5 �C and thus further emphasizing the need for a more accurate temperature reading closer to the gas measuring tube itself so as to ensure a more accurate reflection of the temperature of the hydrogen gas collected. The investigation appears to be riddled with systematic errors that resulted in a somewhat distorted result, with sources of error both working to the increase in percentage yield, and some decreasing it like impurity of reactants. It is as such that future investigations should take into account the above listed sources of error to improve the quality of data collected, and conduct more trials to improve precision. It was found that reacting a piece of solid magnesium ribbon weighing 0.037 g +/- 0.001 with 14.90 cm3 +/- 0.05 of 6 mol dm-3 HCl(aq) in an inverted gas measuring tube, with a holed rubber stopper that had a copper wire cage mounted on it which held in place the solid magnesium ribbon, that 0.00156 mol +/- 2% of hydrogen gas were produced. However, considering the sources of error above, the validity of the statement that 0.00156 mol +/- 2% of hydrogen gas was present in the gas measuring tube after the reaction of solid magnesium ribbon and 6 mol dm-3 HCl(aq) as reacted in the trial, is highly unlikely considering the percentage error and thus the presence of systematic errors. It can be said that the percentage yield of hydrogen gas from the reaction of a piece of Mg(s) ribbon, cleaned with steel wool, weighing 0.037g +/- 0.001 with 14.90 cm3 +/- 0.05 of 6 mol dm-3 HCl(aq) in an inverted gas measuring tube gave a percentage yield of hydrogen gas equal to 104%. ...read more.

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